Copper is drawing much attention as an electrode and interconnect material for integrated sub-micron circuit technology due to its low resistivity and high electro- and stress-mitigation resistance which are superior to Al and Al-alloys. Cu is also a promising candidate to replace Pt due to its low-cost, high conductivity and easier reactive etching properties. However, the successful substitution of Cu into thin-film devices requires the solution to critical issues such as adhesion of Cu layers to Si, SiO2 and ferroelectric layers, Cu diffusion, and elimination of oxidation of the Cu during growth of oxide films. A significant problem is that Cu oxidizes at relatively low temperatures at a significant rate, which results in degradation of the electrical conduction properties of the Cu electrode layers. Thus protection against oxidation is necessary when growing ferroelectric or high permittivity oxide films on Cu electrode layers, since synthesis of those layers requires high temperature and oxygen ambient or oxygen plasmas.
The invention, for preventing oxidation of the copper layer during growth of the oxide layer on the copper layer, is to put down a TiAl oxygen diffusion barrier on top of the copper layer before growing the oxide layer. The TiAl layer absorbs oxygen preferentially binding it to the constituent elements (Ti and Al) of the layer and inhibiting the diffusion of oxygen atoms towards the copper layer while growing the oxide film in an oxygen environment at high temperature. The TiAl oxygen diffusion barrier layer can be deposited by MOCVD, molecular beam epitaxy, atomic layer deposition or physical vapor deposition or any other method suitable for growing oxide thin films.
Various attempts have been made to avoid the problem solved by the present invention, for instance U.S. Pat. No. 6,002,174 issued to Akram et al. Dec. 14, 1999 relates to diffusion barriers but requires the combination of a transition metal such as titanium or aluminum plus silicon plus nitrogen. The patent does not disclose the barrier as effective against oxygen and in fact, nitrogen containing barriers degrade quickly when exposed to oxygen leading to replacement of oxygen in the lattice of the material.
Another attempt at providing barrier materials is disclosed in the McTeer U.S. Pat. No. 6,373,137 issued Apr. 16, 2002. In this patent, McTeer teaches that a TiAl layer is provided but must be annealed in a nitrogen environment to form a TiAl, Cu, N alloy which is susceptible to the same problems associated with the Akram et al. patent. Moreover, as disclosed in the McTeer patent annealing may additionally be performed in an ammonia atmosphere. Accordingly, while various barrier layers have been suggested, none has all the attributes of the amorphous material disclosed herein.